The International Telecommunications Union (ITU) has established guidelines for delivering communication signals from the ground to satellites in orbit (i.e., uplink signals), and for delivering communication signals from satellites to the ground (i.e., downlink signals). In particular, the ITU guidelines allocate a specific uplink frequency spectrum and downlink frequency spectrum for each orbital position (i.e., orbital slot). Thus, for a particular orbital slot, the spectrum bandwidth available for uplink and downlink signals is limited.
Some satellite-based communication systems utilize one or more satellites in one orbital slot to transmit communication signals received from the ground across a wide geographic area. In a typical system, one or more satellites receive communication signals from one or more ground stations (the uplink) via a receive antenna(s) onboard the satellite. These signals are then transmitted over a geographic area (the downlink) via a transmit antenna(s) onboard the satellite. In these systems, the amount of signals that can be handled by the system may be limited by the bandwidth of the spectrum allocated by the ITU for the uplink and/or downlink.
One technique to expand the effective bandwidth of a downlink is to “reuse” some or all of the frequencies in the allocated downlink frequency spectrum. One example of such a system is a “spot beam” satellite system. In such systems, a satellite is capable of transmitting a plurality of spot beams to the ground, where each spot beam illuminates a different “spot” on the ground. If two ground spots are spatially separated, the same frequencies can be reused in the two spots without causing interference. By reusing the spectrum in this way, the effective spectral bandwidth of the downlink can be expanded from the ITU spectrum bandwidth allocation.
But, in order to utilize this expanded spectral bandwidth of the downlink, an equivalent spectral bandwidth should be provided to the satellite via the uplink (assuming a similar signaling format between communication signals in the uplink and downlink). What are needed are techniques for expanding the effective spectral bandwidth of satellite uplinks.